Field of the Invention
The present invention relates to liquid ejection heads and methods of producing the same.
Description of the Related Art
Wire bonding is known as an example of a method of electrically connecting a recording element substrate with an electrical wiring substrate in a liquid ejection head. In the wire bonding, a wire formed of gold, copper, or aluminum is used to electrically connect an electrode terminal on the recording element substrate with a connection terminal on the electrical wiring, substrate.
In the liquid ejection head, the recording element substrate and the electrical wiring substrate may shrink due to changes in their temperatures caused by heat generated while in use or a change in usage environment. The heat shrinkage changes the distance between the recording element substrate and the electrical wiring substrate, applying a stress to the wire connecting the recording element substrate with the electrical wiring substrate. In particular, when the distance between the recording element substrate and the electrical wiring substrate increases, the stress is applied to the wire in a fracture direction (longitudinal direction). This may result in a fracture of the wire.
To solve the problem, Japanese Patent Laid-Open No. 2000-12596 discloses a technique of reducing the fracture of the wire. In the technique, a bonding wire has a large slack portion so as to absorb the stress applied to the wire in the longitudinal direction.
Application of the technique disclosed in Japanese Patent Laid-Open No. 2000-12596 to liquid ejection heads is effective with respect to the stress applied to the wire in the longitudinal direction as described above, but not effective with respect to an external force (load) applied to the wire in a lateral direction. Specifically, if a plurality of wires (wire array) connecting the recording element substrate with the electrical wiring substrate each have a large slack portion, the wires are readily buckled laterally by the load applied in the lateral direction. Thus, the wires adjacent to each other may come in contact with each other, causing a short circuit. Such a problem is particularly caused when a dispenser applies a high-viscosity liquid sealant from an external side of the wire array in a wire array direction in a step of sealing an electrical connection portion, which includes the plurality of wires, between the recording element substrate and the electrical wiring substrate with a sealant. The application of the high-viscosity sealant needs a high pressure. Thus, the sealant ejected through a front end of a dispenser needle squirts from the needle when the pressure is released, resulting in application of a lateral load to the wire located at the end of the wire array.
The present invention provides a reliable liquid ejection head in which bonding wires adjacent to each other are unlikely to be brought into contact with each other by a lateral load applied to the bonding wire, and a method of producing the same.